1. Field of the Invention
The invention pertains to stators for electric motors. It specifically pertains to uniquely designed stators formed by compaction of powdered metallic materials.
2. Description of Related Art
Generally, a brushless dc motor is comprised of a rotor, a stator, windings and a body with endplates to hold the assembly in place. The rotor is generally comprised of a shaft, a magnetic return path and a permanent magnet. A brushless dc motor also has a stator comprised of electrical windings (usually insulated copper windings) that are wound on or embedded into a core material such that once the windings are energized, a magnetic field is formed that interacts with the magnetic field of the permanent magnet of the rotor in a manner such that torque and subsequent rotation is produced in the rotor. Generally, in many embodiments of electric motors, the stator member is cylindrical in shape wherein the rotor member is placed within the stator and held in place by the endplates and bearings. An air gap exists between the outer surface of the rotor and the inner surface of the stator. Electric current is introduced into the windings of the stator such that the stator's core material forms a magnetic path for a magnetic field that simulates rotation about the stator. In other embodiments, the rotor may be fixed with the stator rotating about the rotor.
Stators of the type described above are generally formed by producing thin laminations of high permeability material comprised of a number of alternating teeth and slots that form the inner circumference of the cylinder and an outer yoke material the holds the teeth in position. The thin plates have a thin coat of insulation on their exterior and are stacked together to form the hollow cylinder of the desired dimensions. Insulated electrical windings are then placed in the slots alongside the teeth to form the magnetic field when a current is introduced into the windings. In other known embodiments, similarly shaped stator members may be formed by dynamic magnetic compaction (DMC) with the windings either embedded in the stator material or wound about the stator's teeth after formation of the stator.
Various electrical components such as rotors and stators have been formed using DMC. DMC generally involves metallic powders that are placed into a conductive container. The conductive container is then placed within an electrical coil or otherwise exposed to a magnetic field that is created by an electrical current passing through a conductor. A large current is pulsed through the electrical coil thus creating a very strong magnetic field. This magnetic field will collapse the conductive container and compact the metallic powders into a solid object. U.S. Pat. Nos. 5,405,574; 5,611,139; 5,611,230; 5,689,797; 6,273,963 and 6,432,554 (all assigned to IAP Research, Inc.), each fully incorporated herein and made a part hereof, disclose methods of dynamic magnetic compaction and are related to the formation of electrical components. DMC allows the formation of components of various shapes. DMC also reduces production time as electrical windings may be incorporated into a component during the formation process. Furthermore, DMC produced components may have more efficient magnetic circuits than that of components produced by other means because of the ability of the DMC process to compact the material to nearly full density.
For example, U.S. Pat. No. 5,405,574, “Method for Compaction of Powder-Like Materials, ” was issued to Chelluri et al. on Apr. 11, 1995 from an application filed on Feb. 10, 1992 and is assigned to IAP Research, Inc. This patent is generally directed toward the DMC process and describes methods of producing a wire-like electrically conductive body comprising dense highly compacted particulate material, methods of producing an electrically conductive member, and methods of producing highly dense body superconductive materials.
U.S. Pat. No. 5,611,139, “Structure and Method for Compaction of Powder-Like Material, ” issued to Chelluri et al. on Mar. 18, 1997 from an application filed on Apr. 6, 1995 as a continuation-in-part of an application filed Feb. 10, 1992 that issued as U.S. Pat. No. 5,405,574. This patent is assigned to IAP Research, Inc. It is directed toward structures and devices that utilize dynamic magnetic compaction of powdered material to form high-density bodies of varying shapes and sizes such as rods, tapes, tubes, plates, wheels, etc.
U.S. Pat. No. 5,611,230, “Structure and Method for Compaction of Powder-Like Material, ” issued to Chelluri et al. on Mar. 18, 1997 from an application filed on Jan. 3, 1995 as a division of an application filed Feb. 10, 1992 that issued as U.S. Pat. No. 5,405,574. This patent is assigned to IAP Research, Inc. This patent is generally directed toward the DMC process and again describes a system for producing a body of dense highly compacted particulate material.
U.S. Pat. No. 5,689,797, “Structure and Method for Compaction of Powder-Like Materials, ” issued on Nov. 18, 1997 to Chelluri et al. from an application filed Apr. 6, 1995 as a continuation-in-part of an application filed Feb. 10, 1992 that issued as U.S. Pat. No. 5,405,574. This patent is assigned to IAP Research, Inc. This patent is also generally directed toward DMC and producing bodies, including annular bodies, from powdered materials through DMC.
U.S. Pat. No. 6,273,963, “Structure and Method for Compaction of Powder-Like Materials, ” issued on Aug. 14, 2001 to Barber from an application filed on Jul. 29, 1996 as a continuation-in-part of an application filed on Jan. 3, 1995, now U.S. Pat. No. 5,611,230. A divisional application claiming priority upon this patent has also been filed and was published on Dec. 13, 2001 as U.S. patent application Publication No. 2001/0051104. Both the patent and the published application are assigned to IAP Research, Inc. The patent and the published application disclose “over-pressuring” a powdered material through DMC to densify the material to over 90 percent of its maximum density.
U.S. Pat. No. 6,156,264, “Electromagnetic Compacting of Powder Metal for Ignition Core Application, ” issued to Johnston et al. on Dec. 5, 2000 from an application filed on Oct. 6, 1999. It is assigned to Delphi Technologies, Inc. and is fully incorporated herein and made a part hereof. The patent generally discloses a process for producing a cylindrical electromagnetic core by exposing powdered metals to an electromagnetic field. Among the parts fabricated according to this patent are AC cylindrical electromagnetic parts, such as AC cylindrical electromagnetic ignition coil cores.
U.S. Pat. No. 6,432,554, “Apparatus and Method for Making an Electrical Component,” issued to Barber et al. on Aug. 13, 2002 from an application filed on Feb. 15, 2000 as a continuation-in-part of an application filed on Jul. 29, 1996, now issued as U.S. Pat. No. 6,273,963. A continuation application has also been filed that was published on Aug. 12, 2002 as U.S. patent application Publication No. 2002/0192103. The patent and published application are assigned to IAP Research, Inc. This patent and published application disclose systems and methods wherein powdered materials are placed in a conductive container along with an electrically insulated coil and subjected to DMC to produce a component part, such as a transformer, choke, rotor or stator for an electric motor and the like, with an embedded electrically insulated coil.
U.S. Pat. No. 6,232,681, “Electromagnetic Device with Embedded Windings and Method for its Manufacture,” issued on May 15, 2001 to Johnston et al. from an application filed on Mar. 23, 2000. A divisional application claiming priority upon this patent has also been filed and was published on Jan. 17, 2002 as U.S. patent application Publication No. 2002/0005675. The patent and published application are assigned to Delco Remy International, Inc. The patent is incorporated herein and made a part hereof. The patent and published application disclose a stator core with embedded stator windings manufactured using DMC with radial compaction techniques. The patent and published application also describe a method of fabricating an electromagnetic device, such as a stator, with embedded windings.
U.S. Pat. No. 6,362,544, “Electromagnetic Device with Embedded Windings and Method for Manufacture, ” issued to Johnston et al. on Mar. 26, 2002 from an application filed on Apr. 30, 2001 as a continuation of an application filed on March 23, 2002, now issued as U.S. Patent No. 6,232,681. It is assigned to Delco Remy International, Inc. and is fully incorporated herein and made a part hereof. It describes a cylindrical electromagnetic device with embedded insulated windings comprised of radially compacted powdered magnetic materials.
Other known references related to DMC include U.S. patent application Publication No. 2002/0036367, “Method for Producing & Manufacturing Density Enhanced, DMC, Bonded Permanent Magnets, ” filed by Walmer et al. on Feb. 13, 2001 as a non-provisional application of a provisional application filed on February 22, 2000. In addition, U.S. patent application Publication No. 2002/0043301, “Density Enhanced DMC, Bonded Permanent Magnets, ” filed by Walmer et al. on Feb. 13, 2001 as a non-provisional application of a provisional application filed on Feb. 22, 2000. Both applications were published on Apr. 18, 2002. Each application discloses a DMC method for producing stable, dense, bonded permanent magnets where the binder is inorganic or organic with up to about a 40 percent increase in magnetic saturation performance over magnets formed by traditional methods.
U.S. patent application Publication No. 2002/0117907, “Electromagnetic Pressing of Powder Iron for Stator Core Applications, ” filed Feb. 27, 2001 by Gay et al. It was published on Aug. 29, 2002. It discloses a stator core for an electric motor made of compacted powder material with each particle electrically insulated from one another. For example, the published application describes a stator core to have a density of 98 percent of its theoretical density. The published application also describes methods of manufacturing such a stator core.
As shown above, many electromagnetic devices formed by DMC and methods of forming such devices through DMC are disclosed in existing documents. Specifically, most conventional art discloses the use of DMC to form electromagnetic parts such as stators, rotors, inductors and transformers that contain embedded insulated windings. The documents referenced above disclose stators or rotors with embedded electrically insulated windings or shapes formed of magnetic material through the DMC process; however, conventional stators, whether formed of a series of plates, traditional compaction techniques or by DMC, are generally devices with two-dimensional (non-axial) flux paths having complex winding patterns that require significant motor assembly and manufacturing resources.
Thus, an unsatisfied need exists for an improved stator and methods of manufacture that overcomes deficiencies in the conventional art, some of which are discussed above.